Combination oil refining process



Oct. 9, 1956 F. H. BLANDING COMBINATION OIL REFINING PROCESS Filed Feb. 1,13 1952 /NVENTOQ ATTORNEY 2,765,184 coMBINArioN oir ranrrNrNo rnocnss Forrest H. Blandiug, Cranford, N. J., assignor to Esso Research and Engineering Company, a corporation of Delaware Application February l, 1952, Serial No. 269,535 5 Claims. (Cl. 196,-49)

The present invention relates to the conversion of crude oil into more valuable oil products. More particularly, the invention pertains to an improved oil refining process wherein crude oil is converted into maximum yields of motor fuel and heating oils and minimum yields of relatively' heavy low-value products, such as fuel oils, tar and coke, in greatly simplified equipment.

The broader phases of this invention are directed to the catalytic conversion of crude oil under selected cracking conditions in a first cracking stage followed by distillation of the eluent in a fractionating tower from which a selected bottom fraction is withdrawn. A gas oil fraction is collected in the fractionating tower and passed to a second catalytic cracking stage. The effluent from 'ie second stage is returned to the same fractionating tower. The heat requirements of the process are supplied by burning the carbon formed during the cracking operations.

it has been previously proposed to first distill crude oil to separate virgin naphthas, gas oils and reduced crudes and to catalytically crack the gas oil so separated to produce high octane motor fuels. It has also been a practice to distill the reduced crude under reduced pressure to recover additional catalytic cracking feed stock therefrom. Another refinery practice is to subject gasoline to reforming treatment to improve its octane number.

These various processes carried out separately require separate fractionating towers and separate heating units for each process. in addition, many storage tanks are required for storage of the various products between the various processes. For example, the vacuum distillation equipment used for further distilling the reduced crude obtained from the atmospheric crude still isexpensive to construct, operate and maintain.

It is the principal object of the present invention to provide an improved unitary refining process for the conversion of whole crude oil into maximum amounts of motor fuel and heating oil products in a more simple and economical manner. Other and more specific bjects and advantages will appear from the detailed description hereafter.

ln accordance with the present invention, whole crude is contacted with hot cracking catalyst in an amount suicient to vaporize the gas oil and lower boiling fractions of the crude and to effect substantial cracking of the heavier fractions.

The entire product overhead from this cracking stage is passed into a fractionating tower wherein separation into various fractions is accomplished. The heaviest product from the bottom of the fractionating tower is preferably recycled to the distilling and cracking zone. The gas oil fraction is passed from the fractionating tower to a second catalytic cracking stage to convert the gas oil into motor fuel and other valuable distillate products. The vaporous products of this second cracking stage are returned to the same fractionating tower. Final products such as motor fuels, heating oil and some Fatentod @ch 9, 1%55 2 lighter materials boiling below gas oil are recovered from the fractionating tower. Some of these products may be further treated as later described.

The heat required for the process is supplied by burning carbon off the catalyst in regeneration Zones associated with both cracking stages. One of the important advantages of the invention is the supply of heat both for distillation of the crude as well as the cracking processes by burning of carbon formed on catalyst during the cracking operations.

Other significant advantages are secured when working as outlined above. Heavy products of low value, such as fuel oils or heavy catalytic cycle stocks, may be completely eliminated. One fractionating tower takes the place of several which have been used heretofore to accomplish the same result. All contaminants of the crude are deposited on the catalyst in the first cracking stage. Most tankage for storing intermediate products is eliminated. The whole crude is processed directly to fuel products in a single integrated operation, so that a significant portion of the heat and product losses normally encountered is conserved.

Furthermore, the requirement of gasoline reforming is substantially reduced. The complete destruction of pitch and high boiling cycle stocks in the presence of cracking catalysts to gasoline and heating oil results in a substantial increase of the proportion of catalytic naphtha as percentage of total naphtha in the gasoline pool of the combination process as compared with cracking of the heavy material under non-catalytic conditions. This effect is further enhanced by the fact that some catalytic reforming of the virgin naphtha constituents of the whole crude takes place in the first catalytic cracking stage, so that the octane rating of the virgin naphtha is substantially improved without a separate reforming treatment.

In refining of crude oils it has long been an important object to separate as large as possible an amount of gas oil suitable for catalytic cracking from the heavy residual fractions which contain large quantities of ash components :harmful to cracking catalysts. Deep vacnum distillation, propane deasphalting and other measures have been used for this purpose. The present invention accomplishes this objective without need of such expensive auxiliary equipment. The extent to which fractions of a given boiling range can be distilled overhead in a continuous flash-type distillation is determined by distillation temperature, pressure and the Iamount of residual oil bottoms also present. In this invention, the mild primary cracking step destroys a large fraction, of the order of 70-95%, of the heavy residual bottoms prior to distillation. In addition, the products of the mild cracking, together with the gasoline and other low molecular weight fractions of the crude, are present in the primary flash zone of the large combination fractionator. The presence of these low molecular weight materials greatly reduces the partial pressure of high boiling hydrocarbons at this point, which in turn allows high percentages of the remaining crude oil constituents to be taken overhead in the tower. These fractions can then be cracked in the conventional type second catalytic cracking unit, employing a high quality catalyst relatively free of contaminants. The combination of these features in accordance with this invention allows higher boiling fractions, i. e. fractions boiling up to the boiling level of ll00l200 F., to be distilled in the distillation tower than can be recovered even by a separate vacuum distillation step.

In the present invention, relatively high temperature, but short time, conditions are selected to produce a significant degree of cracking of the highest boiling fractiens of the crude in the rst reactor. This in turn supplies the carbon, the burning of which supplies heat for the primary crude distillation, thereby eliminating need for expensive furnaces for heating the crude oil to high temperature. In addition in the present invention, the specic combination of catalytic reactions together with intermediate distillation of the type specified allows an exceptionally deep distillation of the crude oil constitutents and relining products. This allows subsequent catalytic cracking of unusually large proportions of the remaining products with a high quality catalyst in the reactor.

Having set forth its objects and general nature, the invention will be best understood by reference to the accompanying drawing which is a partly diagrammatic and partly schematic illustration of an apparatus capable of carrying out the invention.

Referring to the drawing, crude oil is supplied to the unit through line 1 and divided into two portions. The major portion (amounting to about 55-90%) is passed through line 3 to preheater 5. The remainder of the cold crude is fed via line 9 directly to a lower portion of fractionator 11. The crude portion passed through preheater may be preheated therein to a temperature of about 40U600 F., preferably about 500-550 F., in heat exchange with hot fractions from the fractionator, hot regenerator ott-gases, or in any other manner known in the art.

The preheated crude leaving preheater 5 is mixed in line 13 with hot regenerated subdivided cracking catalyst and passed to rst stage cracking reactor 15. The feed rate of this hot catalyst is a function of its temperature, the oil preheat and the cracking temperature desired in cracking reactor 15. In any case, sutiicient catalyst should be supplied to vaporize completely the oil While coking unvaporizable constituents on the catalyst and to maintain the substantially dry catalyst-oil mixture in reactor 15 at a cracking temperature of, say, about 850-ll00 F. Suitable hot catalyst feed rates may fall within the range of about 5-30 lbs. of catalyst per pound of total feed to reactor 15 at hot catalyst temperatures of, say, about 10501150 F. which are preferably about 50-200 higher than the desired cracking temperature in reactor 15. If desired, vaporization may be aided by the addition through line 17 of small amounts of steam, say about 1-5% by weight of oil fed.

The catalyst used in the first cracking stage is preferably an activated natural clay or other low-activity cracking catalyst having a cracking activity of about l2-25%, preferably about l5-l8%, D-l-L (D-i-L=distillate|loss; see Ind. Eng. Chem., v. 39, p. illf() (1947); the D-i-L of high activity cracking catalysts is in excess of 25). An average particle size of about 50-10() microns is suitable.

The mixture of cracking catalyst and oil feed is supplied from line 13 to a lower portion of reactor 1S which has preferably the form of a substantially vertical transfer line with a ratio of length over diameter of about 8 1211. The mixture is passed upwardly through this line in the form of a suspension having a density of, say, about 0.5- lbs. per cu. ft. but somewhat higher than that corresponding to the feed ratio of solids and vapors. Linear vapor velocities of about 10-100 ft. per second may be employed. Reactor should be so designed that the oil vapors are retained therein for a relatively short contact time of about l-25 seconds.

At these relatively mild conditions of contact time and catalyst concentration, substantial cracking of heavy feed constituents takes place to form gas oil range hydrocarbons suitable as feed stock for further catalytic cracking. Whatever gasoline is formed is of relatively high octane number. Gas and colte formation, on the other hand, is very moderate, coke deposited on the catalyst amounting usually to less than 4% by weight on oil fed.

The suspension of catalyst-in-oil vapors is passed from reactor 15 into a gas-solids separation system 19 which may consist of a series of cyclone separators and/Qt electrical precipitators of conventional design. Separated catalyst is withdrawn from system 19 through standpipeto combustion in the form of a dense highly turbulent uidized mass M30 separated from an upper disperse phase by an interface or level L30. The apparent density of mass Msn may be about 15-3() lbs. per cu. ft. Carbonaceous catalyst deposits are removed by the heatgenerating combustion. The catalyst is thus regenerated and simultaneously heated to about 1050ll50 F. Flue gases are withdrawn through line 31 to be vented or used for heat exchange in the system. Hot regenerated catalyst is stripped and returned via aerated standpipe 33 to line 13 at the rate and temperature mentioned above.

Circulation of the catalyst between reactor 15 and regenerator 30 is preferably carried out without the use of slide valves employing U-bends 22 and 34 as gas seals. Operations of this type are disclosed and claimed in the Packie Patent No. 2,589,124.

Briey, circulation takes place through two U-shaped pipes, each consisting of a standpipe section through which the solids flow downwardly; a sealing section forming the looped section of the U-tube wherein the pressure is higher than in any part of the system above the sealing section and wherein relatively little gas is needed for aeration; and a riser section through which the solids liow upwardly into the other vessel and into which additional gas is introduced in controlled amounts to regulate the rate of solids ow between the vessels. This transporting gas is introduced a substantial distance above the bottom portion of the U-tube, so that an eective sealing section positioned therebelow contains solids at maximum fluid density which forms a gas seal preventing back flow of gases from one vessel to the other.

Referring to the drawing, separator 19 and regenerator 30 represent the two vessels. standpipe 21, U-bend 22 and pipe 2S are the standpipe section, sealing section and riser section, respectively, carrying solids from separator 19 to regenerator 39. Standpipo 33, U-bcnd 34 and pipes 13 and 15 are the corresponding elements for returning solids from regenerator 30 to separator 19. The normal direction of solids flow is maintained by establishing a pressure differential across each of the U-shaped lines such that the total pressure exerted on the solid in the downow leg or standpipe leg 21 or 33 exceedes the total backpressure exerted on the solid in the upflow or riser leg 25 or 13. This, in turn, is accomplished by maintaining the density of the uidized solid in at least one of the two risers 13 and 25 substantially less than that in the corresponding standpipe section 33 or 21 and adjusting the top pressure in vessels 19 and 33 to compensate for differences in the level of the catalyst beds therein.

The U-bend seals 22 and 34 below the points where gases or vapors are introduced take no part in building up the driving force for solids circulation and operate essentially as gas seal tubes since the pressure generated by the downflowing or standpipe legs of the seals is substantially counterbalanced by the pressure drop on the upowing or riser side of the seal. The extent of the pressure diiferential between the top and bottom of each of the U-bend seals 22 and 34 is determined by the height and density of the iiuidized solids contained therein. This pressure differential, measured from the point of gas injection downward to the bottom of the U-bend, is maintained at a value more than adequate to compensate for normal pressure fiuctuations so as to provide an ade quate safety factor. For further details of this type of solids circulation, the above-mentioned Packie patent may be referred to.

The heat generated in regenerator 30, together with arcanes heat generated in second regenerator 70, is adequate for vaporization and cracking of the preheated feed in reactor and for distillation in fractionator 11 of the vapor efliuent from reactor 15.

In addition to coke, substantial amounts of inorganic ash constituents are deposited on the catalyst in reactor 15. In this manner, reactor 1S acts as a highly effective purification stage for the cracking stock for the second catalytic cracking stage described below. However, these inorganic deposits deactivate the catalyst and this deactivation may not be remedied by combustion regeneration. First stage catalyst, therefore, must be replaced by fresh catalyst at a rate which is relatively high based on the high boiling fractions of the crude. However, based on the entire crude fed the catalyst replacement rate may be held within reasonably low limits of, say, about 0.2-1 lb. of fresh catalyst per bbl. of total crude fed to the system. Such fresh catalyst may be supplied to regenerator via line 3S, while corresponding proportions of spent catalyst may be withdrawn through line 37.

Returning now to separater 19, separated oil vapors are passed via line 39 to fractionator 11 into which the cracked products from the second cracking stage are discharged as later described. The temperature in the bottom of fractionator 11 is controlled by feeding thereto a portion of the cold whole crude via line 9 as described above. in this manner, the temperature in the bottom portion of fractionator 11 below the gas oil trapout tray 41 may be readily maintained at about 700-800 F. to collect the heaviest virgin and cracked constituents in the form of a fraction boiling above 1100l200 F. which may be recycled via line d3 to reactor 15 to be cracked therein to extinction. if desired, a portion or all of the oil in line i3 may be withdrawn through line 45 and recovered as a heavy fuel oil. A heating oil fraction boiling between about 400 and 550600 F. is recovered via line 47 and a heavy naphtha fraction of 250400 F. boiling range is withdrawn via line 49.

Gasoline and hydrocarbon gases are removed overhead through line 51 and passed through a condenser 53 to a gas-liquid separator 55. Liquid gasoline is recovered via line Se and gas via line 59. Additional gasoline may be produced by debutanizing the fractionator overhead and subjectinn the C4 fractions to polymerization. It may also be desirable to subject the product gasoline to thermal or catalytic reforming, hydroforming, 0r other refining treatments adapted to improve the octane rating of the gasoline.

Gas oil boiling between about 550-600 F. and 110V-120W F. is withdrawn from tray 41 and passed via line 57 to second stage catalytic cracking reactor 60. Hot regenerated crack' ig cataiyst is supplied Via line 61 at a temperature and in an amount sufficient to heat the oil to cracking temperature and to maintain the desired cracking reaction. Thi amount may be about 5-25 lbs. of catalyst per lb. of oil in line 61, assuming a catalyst temperature of about lO-ll50 F. and a cracking temperature in reactor 6i? of about 90021000 F. The catalyst is preferably a standard high-activity cracking catalyst, such as a synthetic silica-alumina gel containing about lOJlO wt. percent of alumina and having an average particle diameter of about 50-100 microns. When employing fluid operation, the catalyst hold-up may be about 2-5, preferably about 3 4 lbs. of catalyst in reactor ed per pound of oil to be cracked per hour. Fluidizing gas and vapor velocities of about 0.5-5, preferably about 2 4, ft. per second may be used at pressures of about 04Std p. s. i. g., preferably about 5-15 p. s. i. g.

conventional catalytic cracking and catalyst regeneration system, such as fixed or moving bed, suspensoid or fluid operation, may be employed in the second cracking stage of the process. However, in accordance with the preferred embodiment of the invention, a dense phase iiuid system similar in type to that described with reference to the iirst stage is used. The principal difference between the two systems as illustrated resides in the use of the dense phase cracking reactor 60 with dense phase or bottom drawotf of solids in place of the upow-type transfer line reactor 1S of the first cracking stage. Longer cracking times and higher cracking severities are thus accomplished in the second stage.

Brieiiy, second stage reactor 6d and regenerator 7@ are connected by two U-shaped solids circulation lines. Aerated standpipe 63, U-bend seal and riser section 6? form the line conveying catalyst from reactor 6i) to regenerator 7 0 in substantially the manner described with reference to elements 21, 22 and 25, respectively, air being supplied via lines 69. Carbonaceous deposits are burned otr' the catalyst at conditions similar to those described with reference to regenerator 30, flue gases being removed via line 71. Regenerated catalyst is returned from regenerator '70 via aerated standpipe 72, U-bend seal 73 and line 61, preferably through a conventional distributing cone 7S located in the bottom portion of reactor 60.

Cracked oil vapors are returned via line '75 to fractionator 11, preferably to its bottom portion, to be distilled therein into product distillates, second stage recycle stock (line 57) and recycle bottoms (line 43) as described above. Feeding the cracking product to the fractionator bottom aids in stripping high quality oil vapors from the heavy bottoms fraction and directing lthese clean fractions to reactor 6b rather than rs't stage reactor 15.

The system illustrated in the drawing permits of various modifications. in order to prevent excessive catalyst deactivation in the rirst stage, it may be desirable in many cases to subject the crude to a desalting treatment 'to remove inorganic contaminants. Conventional methods, such as water-washing combined with emulsification and electrical precipitation; solvent deashing; etc. may be employed for this purpose. However, ash contents of, say, about 5-30 lbs. of ash per 1G00 bbls. of crude may be readily tolerated in the iirst cracking stage of the invention.

Other catalysts than those specified may be used in the first stage. For example, a silica-magnesia type catalyst is suitable for this purpose. instead of using two different catalysts in the first and second cracking stages, catalyst withdrawn from the second stage may be used as the catalyst for the first stage. For this purpose, catalyst may be passed from regenerator 7d via line '7'7 to the first stage reactor, fresh replacement catalyst being supplied to the second stage via line '79.

While a fluid dense phase-type rst stage regenerator has been shown, a high velocity transfer line type of regenerator with substantially concurrent flow of gases and solids may take its place. A substantial reduction in first stage catalyst inventory may be secured in this manner.

if the volatility of the product gasoline is too low, a small fraction of heavy naphtha may be branched off line i9 via line 8d and recycled to the second stage reactor' ou for further cracking into lower boiling products. As previously mentioned, the gasoline produced may be further reformed or hydroformed to improve its octane number. In this case, both catalytic cracking stages may be operated at lower temperatures of, say, about 825- 925" F. in order to produce the maximum quantity of naphtha in the catalytic cracking stages without regard to quality. Naphtha quality may thus be controlled in the reforming or hydroforrning stage which is particularly eiiicient for this purpose. The entire reformed product may be returned to the fiash zone of fractionator 1.1 to conserve heat and save a separate fractionator. Other modifications within the scope of the invention will appear to those skilled in the art.

The above description and exemplary operations have served to illustrate specific embodiments of the invention. it will be understood that the invention embraces such other variations and modifications as come within the spirit and scope thereof.

What is claimed is:

1. The process of refining crude petroleum oil, which comprises supplying a minor portion of a stream of whole crude petroleum oil feed to a fractionation zone, preheating the remainder of said oil feed to about 400 600 F., contacting said remainder of said oil feed in a cracking zone at a cracking temperature between about 850 and 1100 F. and as a suspension having a density between about 0.5 and 10 lbs. per cubic foot with a cracking catalyst having an activity of about 12 to 18% D-l-L and preheated at least to said cracking temperature and sufficient in amount to heat said remainder of said oil feed from said oil feed preheating temperature to said cracking temperature and to maintain it at said cracking temperature so as to catalytically crack predominantly gas oil and higher boiling constituents of said remainder of said oil feed in said cracking zone, separating a stream of vaporous cracked products including uncracked crude constituents from used catalyst, burning carbon off said separated catalyst to regenerate and heat the same to said catalyst preheat temperature, returning said regenerated and heated catalyst to said cracking zone, passing said stream of cracked products substantially at said cracking temperature to said fractionation zone at a point below the feed point of said minor portion of crude oil, subjecting said stream in said fractionation zone to distillation by the sensible heat of cracked vapors supplied thereto to produce several fractions including a gasoline fraction, a heavy naphtha fraction, a gas oil fraction and a heavy bottoms fraction boiling above about 1100l200 F. and to separate said minor crude oil portion into similar fractions, returning essentially all of said bottoms fraction to said cracking zone, contacting said gas oil fraction in a second cracking zone at a cracking temperature between about 900 and 1000 F. with a synthetic silica-alumina gel cracking catalyst having an activity in excess of 25% D-i-L and preheated 50 to 200 F. higher than said last-named cracking temperature and sufficient in amount to heat said gas oil fraction and to maintain it at said last-named cracking temperature so as to catalytically crack a substantial portion of said gas oil into gasoline hydrocarbons, separating vaporous cracked effluent of said second cracking zone from said second catalyst, burning carbon off said used second catalyst to regenerate and heat the same to said last-named preheat temperature, returning said regenerated and heated second catalyst to said second cracking zone, passing said separated cracked etiiuent substantially at said last-named cracking temperature to said fractionation zone at a point below the feed point of said rst-named stream of cracked products, subjecting said cracked efuent in said fractionation zone to said distillation and recovering a gasoline fraction from said fractionation zone.

2. The process according to claim l wherein said first named catalyst is an activated natural clay.

3, The process according to claim l wherein at least a portion of said heavy naphtha fraction is passed to said second cracking zone.

4. The process of refining crude petroleum oil, which comprises supplying a minor portion of a stream of whole crude petroleum oil feed to the lower portion of a fractionation zone, preheating the remainder of said oil feed to about 400 600 F., contacting said remainder of said oil feed in a cracking Zone at a cracking temperature and as a suspension with a cracking catalyst having an activity of about 12 to 18% D-l-L and preheated at least to said cracking temperature and sufficient in amount to heat said remainder of said oil feed from said oil feed preheating temperature to said cracking temperature and to maintain it at said cracking temperature so as to catalytically crack predominantly gas oil and higher boiling constituents of said remainder of said oil feed in said cracking Zone,

separating a stream of vaporous cracked products including uncracked crude constituents from used catalyst, burning carbon off said separated catalyst to regenerate and heat the same to said catalyst preheat temperature, returning said regenerated and lheated catalyst to said cracking zone, passing said stream of cracked products substantially at said cracking temperature to said fractionation zone at a point below the feed point of said minor portion of crude oil, subjecting said stream in said fractionation zone to distillation by the sensible heat of cracked vapors supplied thereto to produce several fractions including a gasoline fraction, a gas oil fraction and a heavy bottoms fraction and to separate said minor crude oil portion into similar fractions, returning essentially all of said bottoms fraction to said cracking zone, contacting said gas oil fraction in a second cracking zone at a cracking temperature with a synthetic silicaalumina gel cracking catalyst having an activity in excess of 25% D-l-L and preheated 50 to 200 F. higher than said last-named cracking temperature and sufficient in amount to heat said gas oil fraction and to maintain it at said last-named cracking temperature so as to catalytically crack a substantial portion of said gas oil into gasoline hydrocarbons, separating vaporous cracked etliuent of said second cracking zone from said second catalyst, burning carbon off said used second catalytst to regenerate and heat the same to said last-named preheat temperature, returning said regenerated and heated second catalyst to said second cracking zone, passing said separated cracked eiuent substantially at said last-named cracking temperature to said fractionation zone at a point below the feed point of said first-named stream of cracked products, and below the feed point of said minor portion of crude oil, subjecting said cracked eiuent in said fractionation zone to said distillation and recovering a gasoline fraction from said fractionation zone.

5. The process of refining clude petroleum oil, which comprises separating a whole petroleum crude oil containing inorganic ash contaminants into a major stream and a minor stream, passing said minor stream into the lower portion of a fractionation zone and at a temperature substantially below the first cracking temperature defined below, passing said major stream of crude oil into a cracking zone maintained at a cracking temperature for contact with a relatively low activity cracking catalyst preheated at least to said cracking temperature and sufficient in amount to heat the crude oil to and maintain it at said cracking temperature so as to catalytically crack a substantial portion of said crude oil in said cracking zone to produce vaporous cracked products while depositing carbonaceous material and inorganic ash on the catalyst, separating such vaporous cracked products and vaporous uncracked crude constituents from used contaminated catalyst, burning carbon off said separated used catalyst in a regeneration zone to regenerate and heat the contaminated catalyst to said preheat temperature, returning said regenerated and heated catalyst to said cracking zone, passing said vaparous cracked products and vaporous uncracked constituents substantially at said cracking temperature to the bottom of said fractionation zone below the point of introduction of said minor stream of crude oil, subjecting said cracked products and uncracked constituents in said fractionation zone to distillation by the sensible heat of the vaporous products supplied thereto to produce several fractions including a gasoline fraction, a gas oil fraction and a heavy bottoms fraction, contacting said gas oil fraction in a second cracking zone at a cracking temperature with a second higher activity catalyst cracking catalyst preheated at least to said last-named cracking temperature and suicient in amount to heat said gas oil fraction to and maintain it at said last-named cracking temperature so as to catalytically crack a substantial portion of said gas oil into gasoline hydrocarbons, separating vaporous cracked eftiuent leaving said second cracking zone from said second cracking catalyst containing carbon deposits, burning carbon deposits oi said second catalyst in a second regeneration zone to regenerate and heat the catalyst to said last-named preheat temperature, returning said regenerated and heated second cracking catalyst to said second cracking zone, passing said separated vaporous cracked euent substantially at said last-named cracking temperature to the bottom of said fractionation zone below the point of introduction of said minor stream of crude oil and subjecting said vaporous cracked effluent therein to distillation along with the vaporous cracked products from said first cracking zone and at the same time stripping out lower boiling hydrocarbons from said minor stream of crude oil introduced into the lower portion of said fractionating zone.

References Cited in the tile of this patent UNITED STATES PATENTS Belchetz Aug. 19, 1941 Keith et al. Dec. 9, 1941 Hemminger Oct. 30, 1945 Martin Aug. 27, 1946 Helmers Feb. 25, 1947 Graham et al. Oct. 14, 1947 Loeb Dec. 16, 1947 Delattre-Seguy June 29, 1948 Blanding et al June 15, 1954 

1. THE PROCESS OF REFINING CRUDE PETROLEUM OIL, WHICH COMPRISES SUPPLYING A MINOR PORTION OF A STREAM OF WHOLE CRUDE PETROLEUM OIL FEED TO A FRACTIONATION ZONE, PREHEATING THE REMAINDER OF SAID OIL FEED TO ABOUT 400*-600* F., CONTACTING SAID REMAINDER OF SAID OIL FEED IN A CRACKING ZONE AT A CRACKING TEMPERATURE BETWEEN ABOUT 850* AND 1100* F. AND AS A SUSPENSION HAVING A DENSITY BETWEEN ABOUT 0.5 AND 10 LBS. PER CUBIC FOOT WITH A CRACKING CATALYST HAVING AN ACTIVITY OF ABOUT 12 TO 18% D+L AND PREHEATED AT LEAST TO SAID CRACKING TEMPERATURE AND SUFFICIENT IN AMOUNT TO HEAT SAID REMAINDER OF SAID OIL FEED FROM SAID OIL FEED PREHEATING TEMPERATURE TO SAID CRACKING TEMPERATURE AND TO MAINTAIN IT AT SAID CRACKING TEMPERATURE SO AS TO CATALYTICALLY CRACK PREDOMINANTLY GAS OIL AND HIGHER BOILING CONSTITUENTS OF SAID REMAINDER OF SAID OIL FEED IN SAID CRACKING ZONE, SEPARATING A STREAM OF VAPOROUS CRACKED PRODUCTS INCLUDING UNCRACKED CRUDE CONSTITUENTS FROM USED CATALYST, BURNING CARBON OFF SAID SEPARATED CATALYST TO REGENERATE AND HEAT THE SAME TO SAID CATALYST PREHEAT TEMPERATURE, RETURNING SAID REGENERATED AND HEATED CATALYST TO SAID CRACKING ZONE, PASSING SAID STREAM OF CRACKED PRODUCTS SUBSTANTIALLY AT SAID CRACKING TEMPERATURE TO SAID FRACTIONATION ZONE AT A POINT BELOW THE FEED POINT OF SAID MINOR PORTION OF CRUDE OIL, SUBJECTING SAID STREAM IN SAID FRACTIONATION ZONE TO DISTILLATION BY THE SENSIBLE HEAT OF CRACKED VAPORS SUPPLIED THERETO TO PRODUCE SEVERAL FRACTIONS INCLUDING A GASOLINE FRACTION, A HEAVY NAPHTHA FRACTION, A GAS OIL FRACTION AND A HEAVY BOTTOMS FRACTION BOILING ABOVE ABOUT 1100*-1200* F. AND TO SEPARATE SAID MINOR CRUDE OIL PORTION INTO SIMILAR FRACTIONS, RETURNING ESSENTIALLY ALL OF SAID BOTTOMS FRACTION TO SAID CRACKING ZONE, CONTACTING SAID GAS OIL FRACTION IN A SECOND CRACKING ZONE AT A CRACKING TEMPERATURE BETWEEN ABOUT 900* AND 1000* F. WITH A SYNTHETIC SILICA-ALUMINA GEL CRACKING CATALYST HAVING AN ACTIVITY IN EXCESS OF 25% D+L AND PREHEATED 50 TO 200* F. HIGHER THAN SAID LAST-NAMED CRACKING TEMPERATURE AND SUFFICIENT IN AMOUNT TO HEAT SAID GAS OIL FRACTION AND TO MAINTAIN IT AT SAID LAST-NAMED CRACKING TEMPERATURE SO AS TO CATALYTICALLY CRACK A SUBSTANTIAL PORTION OF SAID GAS OIL INTO GASOLINE HYDROCARBONS, SEPARATING VAPOROUS CRACKED EFFUENT OF SAID SECOND CRACKING ZONE FROM SAID SECOND CATALYST, BURNING CARBON OFF SAID USED SECOND CATALYST TO REGENERATE AND HEAT THE SAME TO SAID LAST-NAMED PREHEAT TEMPERATURE, RETURNING SAID REGENERATED AND HEATED SECOND CATALYST TO SAID SECOND CRACKING ZONE, PASSING SAID SEPARATED CRACKED EFFLUENT SUBSTANTIALLY AT SAID LAST-NAMED CRACKING TEMPERATURE TO SAID FRACTIONATION ZONE AT A POINT BELOW THE FEED POINT OF SAID FIRST-NAMED STREAM OF CRACKED PRODUCTS, SUBJECTING SAID CRACKED EFFLUENT IN SAID FRACTIONATION ZONE TO SAID DISTILLATION AND RECOVERING A GASOLINE FRACTION FROM SAID FRACTIONATION ZONE. 